About Us

Here at HARTLEY CORPORATION we are specialist in heating procesing. At Hartley Sales, our mission is: solutions to heat processing needs. In theory, your requirement is simple — heat transfer will only occur due to one of 3 reasons: convection, conduction, or radiation. In practice, some more complex factors arise — a well designed application will consider:
Material Handling – Heat-Up Time – Production Quantities – Temperature Uniformity – Overtemp Considerations – Safety – Atmosphere Protection – Process Control & Recording – Computer Interface – Testing – Power Requirements – Efficiency – Initial Cost – Cost of Ownership

Very often, a simple batch oven or furnace is the obvious answer. But occasionally we can help in offering novel and creative solutions: e.g., conveyorized systems, selective heating by induction, atmosphere protection, or modification of a standard design.

We have offices in Seattle and Portland, and a long list of satisfied customers from our 60 years of selling and servicing heat processing equipment.  Whether new or used, for large or small applications — we welcome your contact so we can have the opportunity to earn your business.


Guide to Heat Processing Equipment

This guide discusses general issues related to selecting an industrial oven for heat processing. The appropriateness of the guide is evident when you consider that almost all products manufactured today require the application of heat at some point during the manufacturing process.
The complexity of issues related to selecting the optimum equipment for any particular process indicates the need for a universal guide as a starting point.

Process Description

Heat processing applications vary widely from industry to industry. Curing, drying, heat treating, sterilizing and bonding represent just a few of the many requirements for heat processing.

Basic Oven Considerations

Ovens generally are classified as heating equipment operating from ambient to 1000°F
(538° C), Ovens may be designed for intermittent loadings (a batch at a time), or for a continuous flow of work using some form of conveyor. The source of heat is normally derived from steam, hot water, electricity or from combustion of fuel (gas, oil, etc.). Heat can be transferred to the work primarily by natural gravity, forced convection, conduction or by radiant heat sources. Ovens may be designed to contain special atmospheres such as argon or nitrogen, or incorporate special materials of construction to lend themselves to the specific application.

The quantity of material to be processed; the uniformity, size and shape of the products; whether the products lend themselves to logical grouping for batch processing or are better suited to continuous in-line processing; the temperature tolerance that is permissible: these are all issues that must be considered when selecting an oven.

Batch Ovens or Furnaces

Batch-type ovens represent the largest category of ovens used to manufacture products. Batch-type ovens can be classified as cabinet-style or truck-loaded type. The size can range from small bench top units to large industrial installations with thousands of cubic feet.
Bench-mounted and cabinet-type ovens are most often used for laboratory applications such as sterilizing, curing, drying and other general laboratory activities. They range in capacity from 2 to 24 cubic feet. Typical temperature ranges are from 100°F to 650°F (380°C to 343°C). Usually, these ovens are used in lighter duty applications than are industrial production ovens.

Ranging in size from 3 cubic feet interior volume and up, production-type cabinet ovens are used extensively for curing, baking, drying, finishing and annealing processes and an almost limitless number of other applications.

Box-type furnaces are utilized for higher temperature processes (heat treating or annealing). Often a vertical lift door is employed to keep the hot face of the door away from the operator, and for floor space savings.

Continuous Ovens/Furnaces and Material Handling

Continuous ovens include the entire spectrum of oven equipment operated on a continuous or indexing basis. These ovens have construction characteristics that generally are similar to batch ovens. The distinguishing characteristics of continuous ovens include such items as the means of conveyance, air distribution techniques and product loading methods.

Some of the common types of continuous conveyor ovens classified by their method of conveyance are:

Belt conveyors Drag chains
Monorail conveyor Walking-beam conveyors
Pusher conveyors Screw conveyors
Powered roller conveyors

The type of conveyor selected for a continuous oven or furnace depends almost entirely on the type of products to be processed and their configuration at the time of processing. Monorail conveyors are adaptable to a wide variety of workpieces, because many individual workpieces can be positioned on fixtures or racks suspended from the monorail.

Heat-Up/Soak/Cooldown Times

Heat-up, Soak, and Cooldown times are critical elements to consider for selecting the correct equipment. There are three primary design considerations:

  1. What is the required heating capacity to bring the product to the desired temperature within the specified cycle time?
  2. Can the product absorb heat at a rate sufficient to reach temperature within the specified time frame?
  3. Must the heat-up rate be at a controlled rate, or is it sufficient to allow the product to reach temperature as quickly as possible, given the oven’s heating capacity?

Temperature Uniformity

Oven temperature uniformity has different definitions depending on the type of oven and application in question. A basic definition is the overall temperature variation in the oven workspace. Uniformity is generally stated as +/- °F or +/-°C at a given setpoint temperature. The obvious advantage of tight oven uniformities is that all parts within the oven will be subject to the same temperature. therefore insuring consistent product quality.

Oven characteristics that affect uniformity are: wall losses, including through-metal; air distribution and the volume of airflow; control accuracy; oven openings; construction techniques. In order to minimize wall losses, insulation thickness should vary depending on the maximum temperature and uniformity required. Through-metal loss should be kept to an absolute minimum by special panel and unitized construction.

Be sure that oven openings for fresh air and exhaust are strategically located. The location helps to provide a positive pressure differential in relation to the outside of the oven so cool ambient air introduced into the oven through door seals is minimized. The fresh air opening should also be located so that the fresh air can mix thoroughly with the recirculated air.

Similarly, the oven airstream should be designed so air passing through the heating elements is adequately mixed before entering the work chamber. if fresh air is insufficiently mixed with recirculated air, air layers at different temperatures, called air stratification, will affect oven uniformity. (Air duct design, placement and geometry also contribute to uniformity).