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Home  >>  Products  >>  Lab Apparatus  >>  gradient-ovens

gradient-ovens


The gradient-oven is a test apparatus for evaluating the baking and drying behavior of liquid coatings, powder coatings, and resins. The gradient-oven consists of 45 heating elements each micro-processor controlled. Every element has PT-100 temperature probe to precisely record the temperature. A steel test panel is automatically positioned onto the elements. The panel is pressed down for rapid heat transfer.

 

Features

A linear gradient or step gradient can be programmed to precisely determine the cure temperature. The ramp up temperature rate and bake time can also be programmed to similuate production conditions. The gradient-oven can be used for accelerated acid-etch tests. By using the temperature gradient and bake time features a precise evaluation can be performed.

  • Saves time and energy
  • Generates various curing temperatures on one panel
  • Simulates the temperature profile of a production oven in the laboratory
  • Safety devices that comply with the current standards
  • Automatic program control - for precise results

The gradient-oven saves time and money in R & D as well as QC testing of raw materials (e.g. additives, pigments, resins, and coatings). It allows you to simulate the conditions of a production oven in the laboratory by downloading temperature profiles recorded with our temp-gard oven recorder. Thus, material properties, baking conditions and production ovens can be optimized for best quality and economical operation.

Technical Data

Technical Data
Temperature: gradient-oven 250: 30 - 250 °C (86 - 482 °F)
gradient-oven 300: 30 - 320 °C (86 - 608 °F)
Voltage: 230 V, 50/60 Hz
Power Comsumption: 3400 VA
Heating Surface: 20.4 x 3.9 in (520 x 100 mm)
Test Surface: 19.6 x 2.7 in (500 x 70 mm)
Heating Elements: 45 pcs.
Pressure Platform: Traverses automatically (16 kp) for insertion and removal of panel
Linear Gradient: Max. temp. difference between: 30 and 250 (320) °C: 100 °C; 86 and 482 (608) °F: 180 °F
Step Gradient: With 2, 3 or 4 steps: max temp. difference between 2 steps: 50 °C (90 °F)
Heat-Up-Speed 2 °C to 30 °C/min, programmable (3.6 °F/min to 54 °F/min)
Baking Time: In sec. and min.
Memory: Max. 10 gradients
Accuracy: Control accuracy of the heating elements: < ± 2 °C (± 3.6 °F) surface temperatures on 0.8 mm test panels from element 3 to 43:
to 200 ° ± 2 °C (to 392 ° ± 3.6 °F)
to 250 ° ± 3 °C (to 482 ° ± 5.4 °F)
to 320 ° ± 5 °C (to 608 ° ± 9.0 °F)
Measured under specific test conditions.
Dimensions: 18 x 28 x 23 in (465 x 720 x 595 mm)
Weight: 110 lbs (50 kg)
Standards: ISO 2812-5

Use with Iron Oxide Pigments

Temperature stability of iron oxide pigments: Whenever low temperature stable iron oxide pigments are used in baked coating systems or composite materials, it is very critical to define the production window in which the baking temperature will not affect the mechanical, chemical or the optical specifications. The high repeatability and reproducibility of the gradient-oven helps to accurately determine the tolerance range. Depending on the gradient-oven type, coatings can be tested with temperatures up to 320 °C. By applying the coating system with a duplex frame applicator two different coating systems can be applied & tested simultaneously on the same panel. This makes the comparison easier, saving application time and material cost.

Results: Pigment type A starts showing a discoloration at 210 °C, while pigment type B remains color stable up to 250 °C. At temperatures over 280 °C both pigments can no longer be used. The gradient-oven saves you time and money because the testing is considerably shorter than using a convection oven. In addition, the high precision and tight temperature control of the individual heating elements guarantee you reliable and repeatable results - test after test.


Depending on the chemical composition the various iron oxide pigment types show different temperature stabilities:

Temperature Stability of Iron Oxide Pigments
Red Iron Oxide: Up to approx. 1200 °C (2192 °F)
Yellow Iron Oxide: Up to approx. 200 °C (392 °F)
Brown Iron Oxide: Up to approx. 180 °C (356 °F)
Black Iron Oxide: Up to approx. 180 °C (356 °F)

Use with Silicone Additives

Temperature influence on silicone additives: Inter-coat Adhesion In a multi-layer system, like automotive coating systems, silicone additives can diminish the inter-coat adhesion. Silicones have the tendency to migrate to the surface. As they don't have reactive groups, they are not integrated in the coating surface of the first layer. Consequently, they would migrate into the surface of the 2nd layer during application. This type of behavior is known as silicone migration. If the 1st coating layer is baked, reactive groups are created and the silicone additive gets embedded into the resin system of the 1st layer. The capability to migrate is gone which can result in a diminished inter-coat adhesion. The temperature stability of silicones varies depending on how they were modified. The gradient-oven can test the influence of temperature on one panel.

Test procedure: Two differently modified silicones were tested:
Sample A: BYK®-310 - polyester modified polysiloxane
Sample B: Polyether modified siloxane

The application and baking occurred in two steps. For ease of testing the two layers were differently pigmented - 1st layer white and 2nd layer red. The white coating was applied first and baked in the gradient-oven using the step gradient function: 130 °C- 150 °C - 170 °C - 190 °C for 30 minutes. Then the red pigmented coating was applied and baked under the same conditions. The quality of the inter-coat adhesion can be evaluated by using a cross-cut tester with tape, or with knife & tape according to a Ford test specification.

Result according to Ford Test: Sample A shows excellent inter-coat adhesion at all 4 different temperature ranges. In case of sample B the inter-coat adhesion is destroyed at baking temperatures higher than 150 °C. Ford Test Specification: The coating is marked with a knife, adhesive tape is applied to the test surface, pressed on and removed.

Use with 2 Coat Systems

Rewetting of 2 coat systems: At high temperatures silicones can cause wetting problems in a 2 coat application process.

Test procedure: Two differently modified silicones were tested in an amino-cured alkyd topcoat:
Sample A: BYK®-325
Sample B: Polyether modified polysiloxane

For ease of testing the two layers were differently pigmented - 1st layer white and 2nd layer red. The 2 coats were applied wet on wet with a spray gun and each coat had a wet film thickness of 150 µm. The silicone additives were only added in the 2nd coat. Both systems were baked in the gradient-oven using the linear gradient function: 120 °C - 190 °C for 30 minutes.

Result: Sample A was perfectly wetted, while in sample B the two coats "separated" - droplet formation can be seen at higher temperatures. Therefore, sample B can only be exposed to a maximum temperature of 165 °C.

Use with Automotive Topcoat Systems

Chemical etch resistance of automotive topcoat systems: Acid rain, bird droppings, fuel, antifreeze and many other environmental factors can damage automotive finishes. Especially in summertime, some substances can be very aggressive and cause severe damage. Therefore, automotive paint manufacturers as well as auto makers need to find out how different environmental phenomena will interact with a coating system. Throughout the world panels are tested on weathering sites for years to evaluate the influence on color, gloss as well as physical properties. The gradient-oven has been approved by the automotive industry as an accelerated test method. It allows prediction of how a particular coating system reacts to a specific material at increasing temperature levels. This test method is specified by several automotive companies.

The gradient-oven helps to speed up R & D projects saving time and money. In QC testing of baked coating systems the gradientoven produces repeatable results many times faster than using traditional convection ovens.

Test procedure: In a standard test 5 different chemicals can be tested on one panel - e.g. H2SO4 which simulates atmosphere and acid rain, NaOH for car wash detergents, pancreatine (bird dropping), brake fluid, and tree resin. The panels are coated and baked under the specified processing conditions. Using a pipette droplets (approx. 0.05 ml) of these various materials are placed about 6 mm apart vertically on the test panel. Repeat this length down the panel with spacing about every 2-3 cm. The gradient-oven is then programmed to have a linear gradient in the range of 35 °C - 80 °C. The panels are now baked at either 20, 30 and / or 60 minutes to allow for evaluation of the coating. After the baking process the panel is washed under running water, dried and visually evaluated. The evaluation should be done after approx. one hour and again after 24 hours to see if any additional etching has occurred. The temperature is documented at which the first visual changes and damages occurred.

Accessories

  • Self-Adhesive Paper for flat bed printer, for printing reports.
  • Self-Adhesive Strips for flat bed printer, for printing panel marking strips
  • Jig for Powder Coatings is used to facilitate application of powder
  • Glass Plate for gradient-oven, to protect heating bank
  • Test Panels gradient-oven for application of samples for the gradient-oven; made of ST 14 O 5 steel; dimensions: 22.36 x 3.86 x 0.03 in (568 x 98 x 0.8 mm)
  • Film Application Device, solid aluminum construction, 6 knurled screws for secure clamping of test panel during paint application, free floating slide jig holds film applicator
  • Flat Bed Printer for gradient-oven
  • Printer Ribbon for flat bed printer
  • Exhaust Tube Length 98.4 in. (2.5 m); ø 3.1 in. (80 mm)
  • Marking Strip Set Self-adhesive strips for test panels


Application Device


Test Panel with Marking Strip


Film Applicators


Printer with Paper Types


Prices

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Prices subject to change    Prices listed in US dollars for domestic shipments within US, Canada, & Mexico only    Export orders require quotations - click here for a quote     For more info call us 1-800-762-2478 or 954-946-9454.
Item Number Description Prices
2602 gradient-oven 250 $73,841.00
2610 gradient-oven 300 88,298.00
Accessories
2636 Self-Adhesive Paper, Set of 100 sheets for 200 reports 154.00
2637 Self-Adhesive Strips, Set of 100 sheets for 200 marking strips 162.00
2645 Jig for Powder Coatings To facilitate application of powder 295.00
2626 Glass Plate, for gradient-oven,
326.00
2623 Test Panels gradient-oven, Set of 100 461.00
2628 Film Application Device 2,484.00
2630 Flat Bed Printer including accessories 1,900.00
2634 Printer Ribbon 51.00
2621 Exhaust Tube Length, 98.4 in. (2.5 m); ø 3.1 in. (80 mm) 119.00
2622 Marking Strip, Set of 100 121.00



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