PLASTIC

FIELD OF THE INVENTION

The present invention relates to plastic extrusion and in particular to an arrangement for assistance in the quality control of the extruded product.

BACKGROUND OF THE INVENTION

It is well known to extrude plastic products such as pipe and tubing in a host of shapes and sizes. The extrusion process can include the forming of multiple walls in the final product and often the outer walls or one of the walls of the product has been corrugated to add additional rigidity with respect to inward collapse.

The extrusion process includes an extruder which receives the initial plastic material, typically in pellet type form, heats the plastic material, mixes the melted plastic material and provides the melted plastic material under pressure to die tooling. The die tooling divides the molten plastic into one or more streams of plastic appropriately positioned for forming the desired shape. The die tooling often cooperates with a

corrugator that can shape the outer walls of the product and also serves to remove heat from the extruded product to set the plastic before leaving the corrugator.

The supplier of the initial plastic material provides quality control specifications or material specifications of the particular plastic material, however these specifications cannot be realized if the material is extruded. During the manufacturing process the extruder, given that it is applying heat and mechanically mixing the plastic (typically using one or more mechanical screws), the characteristics of the initial supply material have been negatively impacted.

The type of extruder, the operational speed and the condition of the extruder can all substantially contribute to a substantial decrease in the physical properties of the plastic material leaving the extruder. Even extruders of the same model from the same

manufacturer can cause significant differences in the properties of the extruded plastic and this problem is further compounded by both condition and operating parameters of the extruder.

The die tooling divides the product flow and effectively shapes the product flow in a particular manner. The die tooling can also affect the properties of the plastic and the final product. The corrugator shapes the product by use of a series of mold blocks and vacuum forces, also removes heat from the molded product and again the corrugator and the operating conditions thereof can further deteriorate or impact the plastic material properties .

To manufacture an extruded product it is desirable to meet a specified product quality standard with the least amount of material while running the equipment at the maximum or approximate maximum rated speed. These factors substantially influence the cost to manufacture the product.

A further factor affecting the quality of the final product is the addition of additives or fillers. One of the most significant costs associated with the manufacture of extruded product is the initial plastic material costs. It is certainly known to add fillers in an effort to decrease the amount of higher priced plastic material that is used to produce product. Unfortunately, these fillers can also significantly decrease the product characteristics and strength of the final product.

In the manufacture of large diameter corrugated pipe, failure of the final product in the field is an expensive occurrence and difficult to correct. Typically with corrugated pipe, the product has been buried and replacement with new product is not easily implemented without significant disruption and cost. Furthermore the late recognition of off-specification product creates a potential long term liability.

When product quality problems occur, there are a number of different parties that are potentially liable for the deficiencies in the final product. Such

deficiencies could be caused by poor material originally being provided, and as such it would be the manufacturer of the initial material. The operator of the equipment can certainly significantly impact the characteristics of the final product by his particular operation of the equipment and/or an introduction of non-specified fillers in the material.

Even if the initial material is good and the operator has used and maintained all of the various components of the system in their intended manner, the actual extruder can significantly impact the quality of the product. These extruders include large screws which in combination with the extruder heat the product and mix the product to provide a molten flow to the die tooling. This mechanical mixing and heating of the product and the operating speeds thereof can significantly impact the ultimate strength of the final product. Tooling will also affect the characteristics of the final product and lastly the corrugator can affect the product quality.

Testing of the initial material as well as sample testing of the final product is helpful in detecting off- spec product, however problems can still occur.

The present invention seeks to provide a method as well as a particular apparatus to allow for additional testing during the manufacture process to identify deficiencies more quickly.

SUMMARY OF THE INVENTION

A sampling connection for selective sampling of an output flow of an extruder connected to die tooling according to the present invention includes a main channel and a sampling channel. The main channel has an input port and an output port with the sampling channel in fluid communication with the main channel. The input port is connected to and receives an output flow of the extruder and passes the output flow through the output port to connected die tooling. The sampling channel has a closable die outlet through which the output flow of the extruder can be sampled at a position intermediate the extruder and the die tooling.

A sampling connection according to an aspect of the invention includes a closable valve in the sampling channel used to selectively sample the output flow.

In an aspect of the invention, the sampling channel includes a die head with a closable outlet that extrudes a flat ribbon type test sample. According to a further aspect of the invention, the sampling channel is closed by securement of a removable plug and the sampling channel is opened by removal of the removable plug and the subsequent

securement of a test die to the die outlet.

In a further aspect of the invention, the main channel includes a main channel closable valve for selective interruption of the output flow passing through the main channel. Preferably the closable valve is a slide valve.

In yet a further aspect of the invention the sampling channel includes a closable valve that when open connects a die head at the closable outlet to the sampling channel, the die head including an outlet orifice shaped to extrude a flat type test sample.

Preferably the outlet orifice is adjustable to allow adjustment of the thickness of the flat type test sample.

In an aspect of the invention, the sampling channel includes a throttling bushing received in the sampling channel at the closable outlet and the

throttling bushing is sized to restrict the flow through the die head based on an expected output flow of the extruder .

A product quality testing procedure for an extruded product produced by an extrusion process having an extruder providing an output ^* flow to die tooling for forming of the extruded product according to the present invention includes directing a portion of the output flow from the extruder through a sampling die positioned up stream of the die tooling to produce an extruded test strip, and analyzing the test strip to determine material properties of the output flow being provided to the die tooling .

In an aspect of the invention, the product quality testing procedure includes product quality sampling downstream of the die tooling and comparing the material properties of any test strips with the material

properties of the product downstream of the die tooling.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are shown in the drawings, wherein:

Figure 1 is a schematic layout of a plastic extrusion arrangement;

Figure 2 is a front view of a test die;

Figure 3 is a partial perspective view of a test substrate and test specimen;

Figure 4 is a sectional view through a sampling connection;

Figure 5 is a sectional view through an alternate sampling connection with a plug cover secured;

Figure 6 is similar to Figure 5 with a sampling die attached;

Figure 7 and 8 are front view of a sampling die illustrating a variable size port; and

Figures 9 through 11 illustrate sample specimen testing .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 is a schematic of an extrusion molding system 2 where initial plastic material 4 is provided t extruder 6 which heats the plastic and provides molten plastic under pressure to the die tooling 8. The die tooling divides and shapes the flow of the molten plastic and provides the output to a corrugator 10 that assists in forming of the outputted final product 12.

The initial plastic material 4 will have a product specification stating that the plastic has certain minimum characteristics. These characteristics are very significant with respect to the strength and durability of the final product. Based on this specification and with general knowledge of the anticipated decrease in these properties caused by the manufacturing process, the product is determined to meet a product specification. Typically the wall thickness of the extruded product is determined to provide the required strength to exceed the product specification. The initial material

specification characteristics and the characteristics of the final product are not the same as the equipment and the operating conditions of the equipment have

effectively reduced the characteristics of the initial plastic material. The reduction in these characteristics can be as much as 50% or more.

As previously described, present testing includes sample testing of the initial material 4 as well as quality control testing of the final product 12.

If there is an occurrence where the product 12 is not up to the product specification, the issue quickly becomes who is at fault and who is liable for any loss. The typical parties involved in this type of claim include the material supplier, the operator of the extrusion molding system, the manufacturer of the

extruder, the manufacturer of the die tooling, and the manufacturer of the corrugator. Each party's initial defense is to deny any liability. The extruder 6 heats the original product 4 and also mechanically mixes the molten plastic and forces it under pressure to the die tooling 8. This process can significantly decrease the property characteristics and it has been found that the operation of the extruder, the condition of the extruder, and the rate of production can significantly influence the strength of the plastic leaving the extruder.

The die tooling to a lesser extent will influence the characteristics of the molten plastic provided to it however it can be appreciated that the plastic flow must be divided, the flow should be essentially uniform, and certainly the die tooling can also reduce the

characteristics of the plastic or the strength of the final product. The corrugator can also influence the strength of the final product. The corrugator typically imparts the shape to the outer walls of the extruded product and typically this includes a series of

corrugations to increase the strength thereof. In addition, the corrugator cools the plastic to assist in setting of the plastic and the cooling of the product can affect the product characteristics. Lastly, the operator and any influence he may have with respect to the raw material and operation of the equipment must be considered. It is certainly known in an attempt to extend or reduce the amount of initial plastic per unit of product, to include cheaper binders or fillers in the raw material. Such binders or fillers will reduce the characteristics and strength of the final product .

When a product quality failure . occurs in the field, it is indeed expensive and the exact cause of the product quality failure can be difficult to determine. With the present system, a sample plastic strip is taken between the extruder and the die tooling. The sample product can be in a standard flat substrate configuration and test samples can be taken to determine the quality of the molten plastic at the discharge of the extruder. If the product quality is below a certain standard the operator will know that the final product cannot meet the product specification. This arrangement allows early detection of potential product quality issues and allows the operator to adjust the equipment and/or initiate other corrective actions.

The sample substrate strip is shown as 100 in Figure 3 and is extruded through the die port 202 of the slot die 200. The substrate strip 100 can be tested in the known manner by removing a sample 300 of a particular shape which is then analyzed with respect to at least tensile strength, elongation and breakage. In order to sample the output from the extruder 6, a sampling connection 400 is provided between the

extruder 6 and the die tooling 8. The sampling

connection 400 includes a main channel 402 that receives the output from the extruder and directs this output through the main channel to the die tooling 8. The main channel includes an entrance 404 and an exit 406. A plunger or slide valve member 408 is shown in Figure 4 in an open position such that the main channel 402 directs the flow to the die tooling. The sampling connection 400 includes a sampling channel 420 open to the main channel 402. A portion of the molten plastic flow passes through the sampling channel and the slot die 200 having the die port 202. In this way a sample substrate 100 is taken from the output of the extruder as the molten plastic is being provided to the die tooling. The sample channel also includes a slide valve member 424 for opening and closing of the sample channel. It is anticipated that product sampling will only occur from time to time and it need not be constant. The valve member 424 allows closing of the slot die 200 and isolation of the molten plastic from the die.

The sampling connection 400 has been shown with respect to the slot die 200 directed downwardly. It is also possible that this slot die and the sampling connection can be orientated such that the substrate strip 100 is extruded in a horizontal direction.

It is also anticipated in a manufacturing facility that the manufacturer may only need to sample product from the extruder from time to time and may not need the valve member 424. Such an embodiment is shown in Figure 5 where the same sample connection 400 is shown however the die has now been closed with a plug or closure plate 430. The slot die 200 has been removed and is either stored or may be provided on other equipment. In this way a manufacturer can have previously assessed and documented the characteristics of the particular extruder and the operating conditions thereof, for example speed, to determine the impact on the product characteristics. If problems are later detected in the quality of the final product during production it may be necessary to investigate the present output of the extruder at which time the test die could be provided to the sampling connection . Figures 5 and 6 also show a replaceable throttling bushing 422 positioned upstream of the slot die 200.

Various size throttling bushing scan be used to control the flow to the slot die. In this way the slot design can be adjusted according to the output characteristics of the extruder. Figure 6 shows the sampling connection of Figure 5 with the die head 200a attached thereto. Details of an adjustable die head are shown in Figures 7 and 8. In this case the die port 202 is adjustable by movement of the die plate 250 relative to the opposed die plate 252. A relatively large port 202 is shown in Figure 7 and a smaller port 202 is shown in Figure 8. In this way the operator can easily adjust the thickness of the substrate which may be necessary to conduct appropriate product testing .

Figures 9, 10 and 11 show a sample elongation testing of the test strip in Figure 9 to measure the tensile strength and break strength of the sample. As can be seen in Figure 10, the sample will start to neck in the narrowest portion thereof and will eventually break as shown in Figure 11. It has been found that sampling of the characteristics of the product at the exit of the extruder provides good information and insight with respect to the anticipated characteristics of the final product. This substrate testing adjacent the discharge of the extruder in combination with normal product quality testing and initial material testing provides assistance in recognizing product quality control deficiencies at an earlier stage and also

documentation of the product manufacturing process.

Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the invention as claimed.