METHOD AND SYSTEM FOR COATING LEAD COMPONENTS

FIELD OF THE INVENTION

The present invention is concerned with a method for coating of lead components with a coating material.

The invention is also concerned with a system for coating of lead components with a coating material.

The invention is also concerned with a method for coating of a lead shot or similar lead-containing component for marine use with a coating material.

The invention is also concerned with a system for coating of a lead weight or similar lead-containing component for marine use with a coating material.

PRIOR ART

Lead is used as a metal in different technical areas for various applications. One example is divers using lead bricks as weights in order to facilitate submerging. Such weights are in this case arranged in a special weight-belt that might be worn together with a diving suit during diving. Such lead weights are necessary in order to resist the lifting power provided by the diving suit. A advantage of using lead is its relatively high density which makes it suitable for this purpose.

A general disadvantage of using lead is the fact that it is a toxic metal which has a negative effect on both humans and nature. A further disadvantage related to diving is that the lead weights might contaminate the diving suit.

Besides its application in weight-belts for divers lead is used in a plurality of other marine applications, e.g. in lead shots for fishing trawls and other

fishing equipment, as anchors, in keels etc. All these applications of lead as weights result in the environmental disadvantages mentioned above.

There is thus a need for improved components that can eliminate the drawbacks mentioned above in e.g. marine applications.

The environmental problems related to lead also exist in other situations. One example is lead-containing ammunition, e.g. lead pellets which are common in hunting and sports shooting. The lead that comes from lead- containing ammunition and that is spread in nature can result in contamination of ground and water as well as poisoning of birds and animals in case they consume the lead that has been spread in nature. Even if the shooting is performed indoors, there is a risk of negative effects since lead- containing vapours are emitted by the lead-containing ammunition.

Due to the negative effects described above it is common to manufacture lead pellets and other lead-containing ammunition using some kind of coating. For example, patent document US 5189252 discloses coating of lead-containing ammunition using a polymer material in order to minimize the above-mentioned environmental risks.

There is thus a need for improved processes and systems for manufacturing of such lead-containing ammunition that would be environmentally friendly and that would give an easy, cost-effective and reliable coating of e.g. lead pellets with a suitable material.

GENERAL DESCRIPTION OF THE INVENTION

The main purpose of the present invention is to provide a method and a system for coating of various lead components so that the above-mentioned environmental disadvantages can be decreased or preferably eliminated.

This purpose is achieved according to the invention by means of a method of the kind mentioned initially, which comprises the following steps: positioning said lead components inside a container for heating of said lead components; feeding said lead components to a coating tube arranged generally vertically, where a meltable thermoplastic powder is provided in the upper part of said coating tube; feeding hot air towards said thermoplastic powder for generation of a haze of said thermoplastic powder, through which said lead components are brought so that said thermoplastic powder forms a coating on said lead components, where said feeding of air is adapted to maintain a certain amount of said thermoplastic powder mainly floating and define a vertically extending zone inside said coating tube; feeding said lead components through a heating tube for continued heating and melting of said thermoplastic powder so that said coating material is formed; and feeding said lead components to a cooling facility.

The purpose is also achieved according to the invention using a system as mentioned above, comprising a container where said lead components are positioned for heating of said lead components; a coating tube arranged mainly vertically for transition of said lead components, where said coating tube contains a certain amount of a meltable thermoplastic powder; a fan for feeding of hot air towards said thermoplastic powder for generation of a haze of said thermoplastic powder, through which said lead components are brought so that said thermoplastic powder forms a coating on said lead components, where fan is adapted to maintain a certain amount of thermoplastic powder mainly floating, forming a vertically extending zone of thermoplastic powder inside said coating tube; a heating tube through which said lead components are brought, a tube comprising a heating element for continued heating and melting of said thermoplastic powder so that said coating material is formed; and a cooling device for cooling of said lead components.

The invention has several advantages. When the invention is used for coating of lead pellets, a coating that provides an environmentally safe cover on each pellet is formed. Further, the method according to the invention is cost-effective and simple.

A particular purpose of the invention is to be able to create a coating mentioned above on lead components for marine applications, e.g. on lead weights used for diving. In this case a lead component with a coating having several environmental advantages is obtained.

This purpose is achieved through a method for coating of a lead weight or similar lead-containing component for marine application with a coating material, said method comprising the following steps: positioning of said lead weight inside an oven for heating; positioning of said lead weight inside a vat, where a meltable thermoplastic powder is provided; feeding air towards said thermoplastic powder for generation of a haze of said thermoplastic powder in which said lead weight is positioned so that said thermoplastic powder forms a coating on said lead weight; and cooling of said lead weight.

This purpose is also achieved using a system for coating a lead weight or similar lead-containing component for marine application with a coating material, said system comprising: an oven where said lead weight is positioned for heating; a vat where said lead weight is positioned, where said vat contains a certain amount of a meltable thermoplastic powder; at least one fan for feeding air towards said thermoplastic powder for generation of a haze of said thermoplastic powder, in which said lead weight is positioned so that said thermoplastic powder forms a coating on said lead weight; and a cooling facility for cooling of said lead shot.

The concept "lead component" is in this context not limited to lead ammunition, lead weights or other objects for marine applications which in

whole or in part contain lead. Even other details with other application areas than the ones mentioned above should be considered as lead components.

DESCRIPTION OF DRAWINGS

The following is a description of the invention with reference to the enclosed drawings, in which :

Figure 1 is a schematic and simplified view of a system according to the invention for coating of lead components, represented by lead pellets; and

Figure 2 is a schematic view of a system according to an alternative embodiment of the invention.

PREFERRED EMBODIMENT

Figure 1 represents a general drawing of system 1 for coating of lead components according to the present invention.

The system shown in Figure 1 is mainly purposed to be used for coating of lead pellets, i.e. lead-containing ammunition for hunting and sports shooting. However, the invention is generally not limited to methods and systems for coating of lead pellets, but is applicable for other lead details, such as lead bullets or larger items which in whole or in part contain lead. An important application area of the invention is lead components for marine applications, e.g. lead weights, fishing gear, anchors, keels and similar, which is described in details below.

According to the preferred embodiment shown in Figure 1, system 1 comprises a heating device that also constitutes a container for a number of lead components, preferably lead pellets 3. The heating devise preferably constitutes a table 2. The table preferably constitutes a vibrating frying table

on which the lead pellets are heated to a suitable temperature. According to the preferred embodiment of the invention the lead pellets 3 are heated to approximately 220 ⁰ C. Since the table 2 is arranged to vibrate, any changes in the physical shape of the lead pellets 3 are prevented. Further, the table is preferably adapted so that its surface is generally flat, i.e. it is extending horizontally.

Further, table 2 has an opening 4 in one end of the table 2. The opening 4 allows lead pellets 3 to pass through and to fall down towards and inside a first tube 5, which will below be referred to as coating tube. During the coating process for lead pellets 3 according to the invention a certain amount of lead pellets 3 is thus positioned inside the table 2. This results in heating of lead pellets 3 to the desired temperature and feeding the pellets towards the opening 4, whereupon the pellets fall down - in a heated condition - into the coating tube 5.

As an alternative for what is shown in Figure 1 , the invention can comprise other types of feeding facilities, such as tilted surfaces and motor-driven conveyer belts where the lead pellets 3 are positioned.

The coating tube 5 is arranged extending mainly vertically and so that the falling lead pellets 3 are coated with a special powder while falling down under gravitation. According to the described embodiment the powder constitutes a meltable thermoplastic which is marketed and delivered as powder, but which softens and melts upon heating so that a coating on the lead pellets 3 is formed. The powder is preferably "Plascoat PPA 571" (PPA=Performance Polymer Alloy) purchased from Plascoat Systems Ltd., Farnham, Surrey, Great Britain.

Said powder 6 is provided in the upper part of the coating tube 5 according to the invention. This is preferably achieved by using a fan 7 that is adapted to blow air through a feeding tube 8 into the upper part of the coating tube 5.

The airflow is schematically indicated by arrows in Figure 1 , and is directed upwards in order to keep a certain amount of powder 6 floating in the upper part of the coating tube 5. The airflow provided in the coating tube 5 by the fan 7 is preferably heated. This is achieved using a heating device (not shown) that might be positioned in conjunction with the fan 7 or the feeding tube 8. The powder is thus applied by transport of the hot lead pellets through a haze of the powder 6 in the upper part of the coating tube 5. The fan 7 is further adapted to keep a necessary amount of the thermoplastic powder 6 floating on a constant level inside the coating tube 5. A vertically extending zone is thus formed where the powder 6 is positioned. It should be mentioned that the powder 6 should be refilled at the same rate as the lead pellets 3 are fed through the coating tube 5. This can either be done manually or using suitable feeding facilities (not shown).

The speed and the flow for feeding the lead pellets 3 and the thermoplastic powder 6 can be varied and is dependant on the air flow from the fan 7. The amount of powder 6 can not be too small, which would result in incomplete coating of the lead pellets 3, or too large, which can stop the lead pellets in the falling motion through the coating tube 6.

The lead pellets that fall from the table 2 down through the coating tube 5 will thus be covered by the thermoplastic powder 6. The coated lead pellets 3 will subsequently continue the falling motion through the coating tube 5 and towards a second tube 9 that will further be referred to as heating tube. According to the embodiment the heating tube 9 is adapted for continued heating of the lead pellets 3 being coated with powder. In order to achieve this, the heating tube 9 comprises a heating device 10 that preferably is a heating element positioned along the inner wall of the heating tube 9, which is indicated by a dashed line in Figure 1. The lead pellets 3 are thus heated while falling through the heating tube 9. The purpose of this process is to provide a continuous heating in order to ensure a correct melting of powder 6 and to create a uniform coating with proper dimensions on each pellet.

According to the embodiment the heating device 10 is preferably adapted to generate a temperature of approx. 22O ⁰ C.

Subsequent to the completed motion through the heating device 10 inside the heating tube 9, the lead pellets 3 will fall towards a cooling facility 11 that according to the embodiment constitutes a container filled with a coolant, e.g. water. The powder will harden on each pellet 3 upon cooling. An alternative for water-mediated cooling might be air-mediated cooling of the lead pellets 3 in a cooling chamber, or other cooling methods.

Regarding the dimensions of the components in the system 1 can be mentioned that the coating tube 5 preferably has a diameter of approx. 60-80 mm, while the heating tube has a diameter of approx. 200 mm. Further, the total drop height for the lead pellets through the whole system is approx. 2.5 m. These dimensions can of course vary within the present invention. The dimensions of the components can also be adjusted to the amount of lead pellets 3 that is intended to be fed through the system per time unit.

To summarize, the method for coating of lead pellets 3 according to the invention comprises several steps, where the lead pellets 3 are initially heated on the heating table 2 for subsequent feeding through the coating tube 5, where they are coated with thermoplastic powder 6. In order to create the desired coating, the powder 6 is heated so that the lead pellets 3 fall through a haze of powder 6 which is positioned in the upper part of the coating tube 5 by means of the fan 7. The lead pellets 3 are subsequently fed through a heating tube 9 provided with a heating device 10 adapted to heat the powder 6 and the coated lead pellets 3 to create a uniform coating.

Finally, the lead pellets 3 fall down to a cooling facility 11 which provides cooling of the lead pellets 3.

The embodiment according to Figure 1 is based on a method and a system comprising a preheating step (i.e. heating of the lead pellets 3 on the table 2

and by hot air) and a final heating step (i.e. continued heating and melting of thermoplastic powder 6 in the heating tube 9). Further, the lead pellets 3 fall through a tubular device, where the upper part defines a coating tube 5 containing a zone of thermoplastic powder 6 that is kept mainly floating, and where the lower part defines a heating tube 9 where said final heating is performed. An effective manufacturing process is thus established with a relatively high yield of acceptably coated lead components. This high outcome is due to the heating steps on the table 2 and inside the coating tube 5 and the heating tube 9. Since the invention comprises a plurality of sequentially positioned tubes through which the lead pellets 3 fall mainly vertically, an effective manufacturing method is obtained, where parameters such as feeding rate of the lead pellets 3, velocity of the airflow from the fan 7, temperature during different heating steps etc. can easily and predictably be adjusted to obtain the desired amount of coated lead pellets 3.

In the cases when bigger lead components are to be coated, it is sometimes not appropriate to use the system shown in Figure 1 and described above. A method and a system described below and shown in Figure 2 can be used instead. Figure 2 is a schematic drawing of an alternative system V for coating a lead component 3' with a thermoplastic powder described above. This system is appropriate for components considerably larger than lead pellets, more exactly for components with a diameter of one or a few centimeters or more. The lead component 3' can for example be a lead weight for divers or any other lead-containing component that is considered too big to fall through the arrangement shown in Fig. 1. According to the alternative system 1', the lead component 3' is first heated to an appropriate temperature, preferably to 220 ⁰ C. The lead component 3' is than connected to one end of a bar 12 that preferably contains a threaded end part that is inserted into the lead component 3'. The lead component 3' can thus by moved without being touched. A transport cavity is formed in the lead component 3' at the attachment point of the bar 12.

According to the alternative embodiment described in Figure 2, the lead component 3' is positioned inside a separate heating oven (not shown) that provides heating of the lead component 3' to approx. 22O ⁰ C. When the temperature is reached, the lead component 3' is positioned inside a sintering vat 13 that has a shape of a box and contains said powder 6. More exactly, the powder 6 is positioned on a thin mat 14 in the lower part of the vat 13. Powder 6 lays on the mat and creates a cloud or a haze that surrounds the lead component 3' upon immersing. This is achieved by means of at least one, preferably two fans 7 positioned on the bottom of the sintering vat 13. The fans 17 blow air through the mat 14 which creates the haze. The method according to Figure 2 is analogous to the one described above referring to Figure 1 , i.e. it comprises one or two fans with adjustable flow rate which provides floating of powder 6 and creates a zone in the form of a "floating cloud" through which the lead component 3' is brought. The vat 13 comprises also a valve for dry pressurized air from a separate compressor (not shown).

According to the embodiment, the lead component 3' is immersed into the sintering vat 13, which results in creation of a coating of powder 6 on the lead component 3'. Due to hceating, the powder 6 melts and smears on the component 3' forming the desired coating. At normal operation there is no need for a heating device in conjunction with the vat 13.

Subsequently to the coating process, the lead component is dipped into a cooling facility, preferably a vat containing water (not shown), for cooling. The transport cavity formed in the lead component 3' is preferably stopped up by local application and heating of powder 6.

The invention is not limited to the embodiments described above, but can by varied within the scope of the patent claims below. The method according to the invention can be used for coating of a plurality of various components that in whole or in part contain lead, e.g. lead ammunition, boat anchors,

keels and other marine accessories, but also balancing tire weights. Further, dimensions, temperatures etc. of the components in the system can vary within the scope of the invention.

Referring to Figure 1 , it should be mentioned that the invention can be embodied without heating of the lead pellets on the table 2. In this case, the air provided by the fan 7 must be heated to an appropriate temperature for application of the powder 6 on the lead pellets 3.

There are several alternatives to the heating element 10 for final heating in the tube 9, such as gas oil flame, alternatively a heat source of the infrared heating type, alternatively a supply of hot air.